Gel-coated materials with increased flame retardancy

ABSTRACT

The invention provides gel-coated materials that provide enhanced flame-, physical- and chemical-resistance to the foamed materials. The gel coatings can be created with a sol-gel process. Such treated materials can be used, for example, in the manufacture of articles of clothing that are to be used in environments in which fire and exposure to acids, bases or other chemicals which tend to corrode foamed materials is a potential hazard.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/235,569, filed Jan. 22, 1999. now U.S. Pat. No. 6,197,415B1.The invention relates to gel-coated materials suitable for use inapplication is in which flame retardancy is a highly desiredcharacteristic, and methods for fabricating such materials.

The invention relates to gel-coated materials suitable for use inapplications in which flame retardancy is a highly desiredcharacteristic, and methods for fabricating such materials.

BACKGROUND OF THE INVENTION

Materials desirably made fire resistant include polymeric materials,both natural and synthetic, woven and nonwoven fabrics, fibers, mattingand batting. From a chemical structure perspective, low flammability canbe achieved by introducing ring structures, and side groups which arenot readily oxidized. For example, aromatic polyimides show excellentfire resistance, but are too costly for routine use.

A more common approach is to introduce one or more fire-retardantconstituents to an inherently flammable material, such as in the case ofa flammable polymer. The additive can be a fire-retardant monomer whichis copolymerized to some degree with the inherently flammable monomer.Alternatively, the additive can be an unreactive material which iscoated onto the material post-production, or molded or extruded with apolymeric material in a physical blend The inherently flammable materialcould also be reactively treated with a fire-retardant additive afterpolymer production, as in the chlorination of polymers such aspolyethylene.

Compounds which have found use as fire-retardants include inorganiccompounds such as antimony compounds, including antimony trioxide,antimony pentoxide, and sodium antimonate. Boron compounds such as zincborate, boric acid and sodium borate. Alumina trihydrate and molybdenumoxides are also useful inorganic compounds.

Halogenated compounds have also been used, including decabromodiphenyloxide, chlorendic acid, tetrabromophthalic anhydride, and similarlyhalogenated compounds. These halogenated compounds, especiallychlorinated compounds, are often combined with the above-mentionedinorganic compounds, especially antimony-, iron-, cobalt-, nickel-,molybdenum-, and other metal-containing compounds, to producesynergistic fire-retarding effects.

SUMMARY OF THE INVENTION

The invention uses gel coatings on base materials to greatly increasethe fire retardance of such materials. The gel coatings can be producedthrough sol-gel processing of foamed materials. The gel coating providesa degree of physical and flame protection for the materials thusproduced. The oxidative resistance of such materials is unimproved aswell. The coating is believed to minimize oxygen contact with thematerial. This can result in reduced incidence of oxidation fromatmospheric oxygen for the materials, or any components contained withinthe materials, for example, reduced flammability for flammable contents,or reduced chemical oxidation for atmospheric oxidation-sensitivecontents. The contents which can be included in the gel-coated materialsinclude phase change materials in various forms.

The invention further provides a method for providing a gel coating on amaterial by a sol-gel process.

The invention provides flame-retardancy without altering the physicalprocessing of the material, while undesirable alteration is commonly thecase when inert halogen-containing additives are added. The gel-coatedmaterials of the invention possess excellent light stability, incontrast to many halogen-based and phosphorus-based flame-retardantmaterials. The thermal stability of the gel-coated materials of theinvention is at least as high as the untreated material; this is oftennot the case for halogen-based flame-retardant materials, which canproduce corrosive hydrogen halides upon exposure to heat. The density ofthe gel-coated materials of the invention is lower than that ofhalogen-containing fire-retardant materials. The invention provides agel-coated material having permanent fire-retardant properties.

The gel-coated materials of the invention are noncombustible, maintaintheir integrity upon exposure to flame, and seal the material completelyfrom fire. The gel coatings are easily applied, and can easily bemodified, with, for example, coloring agents. The gel coatings arerepeatedly washable with commonly available solvents, and thefire-retardancy is retained upon such repeated washing.

The gel-coated materials of the invention possess excellent hydrolyticand chemical resistance, whereas phosphorus-containing flame-retardantmaterials generally do not.

Base materials generally described are adapted to be placed withinarticles of clothing including footwear and various articles ofprotective clothing designed for environments of extreme temperature andhazard from fire. According to the invention, a base material such as afoamed polymer, fiber, woven or nonwoven fabric, batting or matting iscoated with a gel coating. The gel coating can also provide increasedresistance to chemical reactants such as acids, bases and otherchemicals that can damage or dissolve foamed materials. Such materialsare ideal in protective clothing, for example, fire fighting suits.Gel-coated foamed materials are suitable for flame-resistant cushionsused in aircraft, automobiles, furniture and other cushioned articles.Fabrics, matting and batting are other applications for which theinvention is suited.

The gel-coated materials of the invention can also contain heat controlagents, such as those which store latent heat. Such heat control agentsinclude phase change materials, which can be integral to the basematerials or gel coatings of the invention.

For the purposes of this specification, metal oxides, and metalalkoxides also include those materials which are calcinable (orotherwise oxidizible) to metal oxides, and metal alkoxides, as describedbelow. For the purposes of this specification, calcination includesoxidation processes in general.

A flammable base material can be inherently flammable, or can becomeflammable upon the introduction of flammable materials in the interioror exterior of the base material.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entirety. In case of conflict, the presentspecification, including definitions will control. In addition, thematerials, methods and examples are illustrative only and not intendedto be limiting.

DETAILED DESCRIPTION

The gel-coated materials of the invention feature base materials coatedwith a gel, specifically a gel produced by sol-gel processing. The gelcoating provides flame-, physical- and chemical-resistances to thecoated material, resulting in enhanced performances in criticalapplications. The materials which are coated with a gel can be fabrics,fibers, matting, batting or polymeric materials. Useful polymericmaterials can be foamed polymeric materials, for example, foaminsulation layers of footwear or garments.

The burning of polymeric materials is highly influenced by the densityof materials in general. Most unexpanded plastic polymers have densitiescommonly in the range of at least 0.7 g/cm³ and at most 1.5 g/cm³. Onthe other hand, foamed polymeric materials have densities of about 0.03g/cm³, so that only a few percent (typically less than 5%) of the totalvolume of these foams is solid polymer. The presence of so much gas inthe structure of a foamed polymer influences the burning characteristicsgreatly.

The exposure of a large surface area to the oxygen present in airresults in an increased rate of burning. On the other hand, since theamount of potentially flammable material per unit volume is relativelysmall, the heat available for flame propagation per unit area isrelatively low. Also, for thermoplastic foams such as polystyrene foam,rapid melting results from the heat of flames. This causes the foam torecede rapidly from the flame, and the spread of flame is minimized, orthe material is self-extinguishing.

Thermoset foams, in contrast, are highly crosslinked. Flame does notcause them to melt appreciably, so that the material does not recedefrom the advancing flame front. If the thermoset foam is intrinsicallyflammable, a rapid ignition of the entire foam can ensue.

There are five fundamental ways to increase the fire-retardance ofpolymeric base materials: increase the crosslinking density of thepolymeric base material to increase its decomposition temperature;replace material which can serve as fuel with material that cannot serveas fuel in the polymeric base material, by adding inert fillers, halogensubstituents, or inorganic constituents; induce the polymeric basematerial to flow when ignited by interrupting the polymer backbone,thereby allowing the polymer to drip and recede from the flame front;introduce pathways which allow alternate means of decomposition, forexample pathways which lead to carbon charring; and mechanical meanssuch as a non-flammable skin bonded to the surface of the polymeric basematerial, covering the polymer with an intumescent or nonintumescentcoating, or simply installing a sprinkler system proximate the polymericbase material.

Fire-resistant coatings are generally of two types, intumescent andnonintumescent. Intumescence is the expansion of a coating into afoamlike carbonaceous char upon heating. Continuous heating ofintumescent coatings pyrolyzes them into heat-resistant carbonaceousfoam-like coatings.

The coating used to coat the foamed polymeric materials of the presentinvention is a gel coating. Specifically, the gel is prepared by aprocess known as the sol-gel coating process. A colloid is a suspensionin which the dispersed phase is not affected by gravitational forces,due to the dimensions of the dispersed phase (1-1000 nm). A sol is acolloidal suspension of solid particles in a liquid. A gel can beconsidered to be the agglomeration of these particles into a structureof macroscopic dimensions, such that it extends throughout the solution.It is, therefore, a substance that contains a continuous solid skeletonenclosing a continuous liquid phase.

Sol-gel processing according to this invention involves chemicalprocessing of gel precursors to prepare a colloid. These gel precursorsconsist of metal atoms surrounded by ligands. The metal atoms and theligands fall into wide classes described below.

Generally, chemical processing of the gel precursors involves hydrolysisand condensation reactions in which the ligands of the precursors arereplaced by bonds to the ligands of other metal or metalloid elements.This process results in a growing network of metal or metalloid elementslinked together, eventually forming a gel.

The gels for use in the invention can be prepared via reactions whichuse monomeric, metal oxides as gel precursors. Metal oxides for use insol-gel processing are generally represented by M(—OH₂)_(n) (aquoligand), M(—OH)_(n) (hydroxo ligand), and M(═O)_(n) (oxo ligand), whereM is the metal atom, and n depends on the coordination state of M. Metaloxides for use in such reactions include TiO₂, ZrO₂, RuO₂, RuO₄, V₂O₅,WO₃, ThO₂, Fe₂O₃, MgO, Y₂O₃, HfO₂, Nb₂O₅, UO₂, BeO, CoO, NiO, CuO, ZnO,In₂O₃, Sb₂O₃, Al₂O₃ and SnO₂. Mixtures of such oxides are also useful,such as ZnO—TiO₂, TiO₂—Fe₂O₃, SnO₂—TiO₂, Nd₂O₃—TiO₂, Al₂O₃—Cr₂O₃,MgO—Al₂O₃, MgO—TiO₂, MgO—ZrO₂, ThO₂—UO₂, ThO₂—CeO₂, Bi₂O₃—TiO₂,BeO—Al₂O₃, TiO₂—Fe₂O₃—Al₂O₃, Al₂O₃—Cr₂O₃—Fe₂O₃, PbO—ZrO₂—TiO₂,ZnO—Al₂O₃—Cr₂O₃, Al₂O₃—Cr₂O₃—Fe₂O₃—TiO₂, and ThO₂—Al₂O₃—Cr₂O₃—TiO₂. Itis also within the scope of this invention to use dispersions or sols ofthe ceramic metal oxides in combination or admixture with dispersions orsols of one or more metal oxides which are unstable in normal airenvironment (such as Li₂O, Na₂O, K₂O, CaO, SrO, and BaO) and/or ceramicoxides having an atomic number of 14 or greater (such as SiO₂, As₂O₃,and P₂O₅), representative combinations including Al₂O₃—Li₂O, TiO₂—K₂O,ZrO₂—CaO, ZrO₂—Al₂O₃—CaO, ZrO₂—SrO, TiO₂—BaO, B₂O₃—SiO₂, TiO₂—ZrO₂—BaO,Al₂O₃—Na₂O, TiO₂—SiO₂, MgO—SiO₂, Fe₂O₃—BaO, ZrO₂—SiO₂, Al₂O₃—As₂O₃,ZrO₂—P₂O₅, Al₂O₃—SiO₂, Al₂O₃—B₂O₃, and Al₂O₃—Cr₂O₃—SiO₂.

Instead of using the precursor material in the form of dispersions orsols of the oxides, it is within the scope of the invention to use theprecursor materials in the form of water soluble or dispersibleinorganic or organic compounds which are calcinable, or otherwiseoxidizible, to the corresponding metal oxide or metalloid oxide. Thesecompounds representatively include many carboxylates and alcoholates,e.g., acetates, formates, oxalates, lactates, propylates, citrates, andacetylacetonates, and salts of mineral acids, e.g., bromides, chlorides,chlorates, nitrates, sulfates, and phosphates, selection of theparticular precursor compound being dictated by availability and ease ofhandling. Representative calcinable precursor compounds useful in thisinvention include ferric chloride or nitrate, chromium chloride, cobaltnitrate, nickel chloride, copper nitrate, zinc chloride or carbonate,lithium propylate, sodium carbonate or oxalate, potassium chloride,beryllium chloride, magnesium acetate, calcium lactate, strontiumnitrate, barium acetate, yttrium bromide, zirconium acetate, hafniumoxychloride, vanadium chloride, ammonium tungstate, aluminum chloride,indium iodide, titanium acetylacetonate, stannic sulfate, lead formate,bismuth nitrate, neodymium chloride, phosphoric acid, cerium nitrate,uranium nitrate, and thorium nitrate.

The sol-gels for use in the invention can also be prepared via reactionswhich use monomeric, metal alkoxide precursors. This class of compoundsis represented by M(OR)_(n), where M is a metal, OR is an alkoxide (analkoxide with from one to six carbons which may be further substituted),and n is from 2 to 8, depending on the coordination state of the metal.The metals used in the metal alkoxide precursors are Ti, Cr, W, Th, Fe,Mg, Y, Zr, Hf, V, Nb, U, Be, Co, Ni, Cu, Zn, In, Sb, Al, Sn and Si. Thealkoxy ligands are generally alkoxides with from one to six carbons suchas methoxy, ethoxy, propoxy, butoxy, pentoxy, and hexoxy ligands, orsubstituted or unsubstituted aryloxy groups. oligomeric precursors canbe used such as ethoxypolysiloxane (ethyl polysilicate),hexamethoxydisiloxane (Si₂(OCH₃)₆) and octamethoxytrisilioxane(Si₃(OCH₃)₈).

The monomeric, tetrafunctional alkoxysilane precursors are representedby the following formula.

where RO is a C₁-C₆ substituted or unsubstituted alkoxy group, or asubstituted or unsubstituted aryloxy group. Typical examples includemethoxy, ethoxy, n-propoxy, n-butoxy, 2-methoxyethoxy, and phenylphenoxygroups. Ethoxypolysiloxane (ethyl polysilicate), hexamethoxydisiloxane(Si₂(OCH₃)₆) and octamethoxytrisilioxane (Si₃(OCH₃)₈) can also be used,as well as the cubic octamer (Si₈O₁₂) (OCH₃)₈. Organically modifiedsilicates having various organic ligands can be used, such as thoseformed by combining tetraalkoxysilanes with alkyl-or aryl-substitutedand organofunctional alkoxysilanes. Organic functionality can beintroduced to the alkoxy ligands with substituents such as—(CH₂)_(n1)NH₂, —(CH₂)_(n1)NHCO—O—NH₂, —(CH₂)_(n1)S(CH₂)_(n2)CHO, andlike substituents, where n1 and n2 are from 0 to 6. Polymerizibleligands can also be employed, such as epoxides, to form organic networksin addition to an inorganic network. Choice of precursor can be madeaccording to solubility or thermal stability of the ligands.

To produce gels with somewhat less dense structure, to impart moreorganic character to the gel, or to allow for derivitization,organotrialkoxysilanes (R′Si(OR)₃) or diorganodialkoxysilanes(R′₂Si(OR)₂) can be used as gel precursors. The groups R′ need not bethe same as each other on a given precursor molecule. Examples of suchprecursors are methyltriethoxysilane, methyltrimethoxysilane,methyltri-n-propoxysilane, phenyltriethoxysilane, andvinyltriethoxysilane.

Catalysts are optionally but generally present in sol-gel processing.Acids and bases are suitable catalysts for sol-gel processing as carriedout in the invention. Such catalysts facilitate both hydrolysis andcondensation reactions, and can play a role in product structures.Preferred catalysts include inorganic acids (e.g., hydrochloric, nitric,sulfuric and hydrofluoric acid), amines including ammonia and ammoniumhydroxide, organic acids (e.g., acetic acid), bases (e.g., potassiumhydroxide), potassium fluoride, metal alkoxides (e.g., titaniumalkoxide, vanadium alkoxide). All other factors being equal, acidcatalysis produces gels which are cross-linked to a lesser extent thangels produced by base catalysis. A suitable catalyst for the sol-gelprocessing reactions of the invention is nitric acid.

Sol-gel processing can take place in the presence of solvents. Suitablesolvents include water, alcohols (e.g., methanol, ethanol), amides(e.g., formamide, dimethylformamide), ketones (e.g., acetone), nitrites(e.g., acetonitrile), and aliphatic or alicyclic ethers (e.g., diethylether, tetrahydrofuran, or dioxane). These solvents can facilitatehydrolysis reactions as described below, especially if the ligandspresent on the sol-gel precursor molecules are bulky, such asphenylphenoxy ligands.

Inasmuch as water is often a reactant involved in sol-gel processingreactions, as in the hydrolysis reaction described below, it is includedin the list of solvents to the extent that water in excess of astoichiometric minimum amount is provided. Solvents other than water aregenerally employed to prevent phase separation in those sol-gelprocessing reactions which involve water-immiscible components. Controlover the concentration of the reactants is also provided through the useof a solvent.

The first reaction generally taking place is hydrolysis, in which thealkoxide ligands of the alkoxysilanes are replaced by hydroxide ligands,from water. This reaction is represented here.

where RO is a C₁-C₆ substituted or unsubstituted alkoxy group, orsubstituted or unsubstituted aryloxy group. The product of this reactionis an alcohol, reducing the need for alcohol or other mutual solvents asthe reaction proceeds. Since the reaction is reversible, the alcohol canalso participate in reverse reactions, reesterification andtransesterification. All substituents attached to silicon are labile,and populations of substituents will depend in an equilibrium sense oncontrol exerted over the concentrations of alcohol and water, the typeof catalyst used and the extent of reaction.

Under acid-catalysed hydrolysis conditions, the alkoxide ligand islikely to be protonated as a first step, making it a better leavinggroup as water attacks from the backside of the central silicon atom.Seemingly for this reason, steric effects of the ligands play asignificant role in determining the rate of this reaction. Underbase-catalysed hydrolysis, dissociation of water to produce hydroxideion likely takes place. The hydroxide attacks the backside of thecentral silicon atom, displacing the alkoxide ion. Inductive effects ofthe ligands are likely to be important here since the silicon atomdevelops charge in the transition state.

The subsequent condensation reactions can either be between Si—OR andSi—OH or between two molecules of Si—OH to produce a silicate gel asshown in the following reactions.

The mechanism of silicate gel formation is distinct from that of organicpolymers, in that the silicic acid (Si(OH)₄) polymerizes into discreteparticles. These particles then aggregate into chains and networks. Theresulting macroscopic structure of the gel can be characterized aseither a dense network with well-defined solid-liquid interfaces, auniformly porous network, or an open network.

This gel is then desirably applied to a base material, and dried toeventually produce a glassy material. Dried gels are referred to asxerogels or aerogels Xerogels are produced by evaporation of liquid,while aerogels are dried by supercritical extraction of solvent. Duringthis phase of the process, consolidation of the gel occurs. This processis also referred to as curing. The rate of curing gives control over theporosity of the resulting gel coating.

The gel initially tends to shrink as liquid is removed, through removalof liquid at the surface of the gel. The amount of shrinkage that occursinitially is dependent both on how the gel is produced and how it isdried. Drying by evaporation of solvent produces xerogels which aredenser than aerogels produced by supercritical extraction of liquid.

At pH values below about 2, hydrolysis reactions involve protonatedalkoxide groups and the rate of hydrolysis is large compared to the rateof condensation. The supply of precursor monomers is essentiallydepleted at an early point in the condensation reaction. Resultingcluster-cluster aggregation leads to weakly branched structures. AbovepH of about 7, hydroxide and SiO⁻ ions are the reactive species inhydrolysis and condensation reactions, respectively. If at leaststoichiometric ratios of water to gel precursor are used ([H₂O]/[Si]≧4),more compact and highly branched structures result as described inBrinker et al. Sol-Gel Science, Chapter 3.

Thus, gels produced through acid-catalysis are cross-linked to a lesserextent. Such gels shrink more during initial drying because thestructures can interpenetrate each other more. The pores in such a gelare smaller, so that capillary pressure which is exerted during finalstages of drying further compacts the structure. The resulting gel ischaracterized by an extremely fine texture.

The pores in gels produced by acid-catalysis and drying by evaporationrange in size from 10 to 50 Å.

According to the invention, gel coatings of metal oxides, metalloidoxides or the compounds calcinable (or otherwise oxidizible) to suchoxides (such as those listed above) are produced on the surface of abase material. The gel coatings desirably provide a continuous coatingon the surface of the base material.

As an example, the base material can be a foamed polymeric material.This material can be hydrophobic, hydrophilic or amphipathic. Exemplaryof acceptable polymers are polyurethane, polypropylene, butyl, silicone,cellulose acetate, neoprene, epoxy, polystyrene, phenolic, and polyvinylchloride. Foams such as styrofoam are not particularly well suited forthe gel-coatings of the invention, and are not preferred. The foamedmaterial should not react appreciably with the sol used to produce thegel in such a way as to structurally weaken the foamed material. Limitedchemical reaction with the surface of the foamed material may takeplace, and in fact may be beneficial in certain applications, forexample, on silicon foam. Preferred are materials such as a moldablefoamed organic plastic. The foamed materials need not be inherentlyflammable. Foams such as silicon foams are not inherently flammables butif a flammable material is contained within the interior, or on thesurface of, a non-flammable foam, a gel coating is useful.

The gel coatings of the invention are equally useful with open- orclosed cell foams. For applications in which the foam is desired to bebreathable, an open cell foam is preferred. An open cell foam structurealso allows for the possibility that the entire foam can becomeimpregnated with the gel coating. In such cases, uncured sol can beremoved by squeezing the open cell foam after it has been soaking in thesol to clear air passages and allow the foam to remain breathable. Opencell foams with particularly fine cell structure could becomeimpermeable in this way, however, as the air passages could conceivablybecome solidified. Foams with closed cell structures will only have gelcoatings on their exposed surfaces, since the uncured sol will notpenetrate to the interior of a closed cell foam. The choice of open orclosed cell foam is made based on the particular application. If a highlevel of flame resistance is necessary, an open cell foam is preferred,as it will absorb a much greater amount of sol than a closed cell foam.If the foam is required to remain relatively lightweight, a closed cellfoam may be better, since its interior will remain as an uncoated foam.This also makes the bulk properties of gel-coated closed cell foamssimilar to those of uncoated closed cell foams, since the vast majorityof the foam is unaffected by the coating, and its physical propertiesare largely retained.

The base material can also be a fabric. Suitable fabrics include thosetypically used for clothing materials, such as natural fabrics,including cotton, linen, wool, hemp, jute, ramie, silk, mohair, vicuna,and the like. Other fabrics include man-made fabrics such as organicpolymer fabrics including rayon, viscose, acetate, azlon, acrylic,aramid, nylon, olefin, polyester, spandex, vinyon and the like. Suchfabrics can be knitted, woven or nonwoven. The base material may also bethe fibers or filaments of the materials listed above which are composedof fibers or filaments. In either case, the gel coating is applied inessentially the same way as described for polymeric materials and foamedpolymeric materials.

Such base materials, in addition to themselves having a potential forflammability, may contain other desirable constituents which areindependently flammable, and may render an otherwise nonflammable basematerial flammable by virtue of their flammability. In such cases, thegel-coated materials of the invention also provide protection againstflame.

Such desirable constituents which may be present in a base materialinclude materials which can absorb heat and protect an underlyingmaterial from overheating. Thermal energy is absorbed by the phasechange of such materials without causing an increase in the temperatureof these materials. Suitable phase change materials include paraffinichydrocarbons, that is, straight chain hydrocarbons represented by theformula C_(n)H_(n+2), where n can range from 13 to 28. Other compoundswhich are suitable for phase change materials are2,2-dimethyl-1,3-propane diol (DMP),2-hydroxymethyl-2-methyl-1,3-propane diol (HMP) and similar compounds.Also useful are the fatty esters such as methyl palmitate. Preferredphase change materials are paraffinic hydrocarbons.

Such constituents can be encapsulated, as is desired in the case ofphase change materials. Such encapsulated constituents can further beencapsulated in microcapsules. The microcapsules can be made from a widevariety of materials, including polyethylene, polypropylenes,polyesters, polyvinyl chloride, tristarch acetates, polyethylene oxides,polypropylene oxides, polyvinylidene chloride or fluoride, polyvinylalcohols, polyvinyl acetates, urethanes, polycarbonates, andpolylactones. Further details on microencapusulation are to be found inU.S. Pat. Nos. 5,589,194 and 5,433,953. Microcapsules suitable for usein the base materials of the present invention have diameters from about1.0 to 2,000 microns.

Such constituents can be introduced to the base materials pre- orpost-manufacture, that is, before or after the material is formed in itsfinal state. This depends on the nature of the constituent, and whetherit can survive the manufacturing or processing of the base material andstill retain its desired function, or whether the manufacturing orprocessing can impart new and desired functionality to the constituent.

For example, if a microencapusulated phase change material is to beintroduced into a foamed polymeric material, it could be dispersedthroughout the polymeric material prior to the foaming of the polymer.In some embodiments, the microencapusulated phase change material couldbe dispersed throughout the polymeric material so that it forms aproduct in which the microcapsules are individually surroundinglyencapsulated and embedded within the base material. Alternatively, suchphase change material could be pressed directly into the foam after itis made, for example, by pressing the microcapsules into the foam withan applicating instrument. Gel coatings can be formed on base materialscontaining various loadings of phase change containing additives. Thefire-retardant capabilities of the sol-gel can suppress the flammabilityof any flammable phase change materials.

The invention also provides a method for producing gel-coated materials,by the method of sol-gel processing. In general, base materials asdescribed above are mixed with a sol which is allowed to cure into agel.

Sols are generally prepared by mixing metal-containing gel precursor andsolvent together in a precursor/solvent ratio which can vary from about3:1 to about 5:1 by volume. Preferably, the precursor/solvent ratiovaries from about 3.5:1 to about 4.3:1. Separately, catalyst and waterare mixed in a catalyst/water ratio which can vary from about 1:12 toabout 1:22 by volume. The two solutions are mixed together withstirring.

As the mixture warms and subsequently cools, the onset and completion ofreaction is indicated. At the completion of reaction, the mixture iscontacted with a base material surface. The mixture can be sprayed ontothe material, brushed onto the material, or the material can be dippedinto the sol.

Spraying of the sol onto an article is however, less likely to result ina continuous coating on the base material surface. A sprayed sol islikely to cure more rapidly than a brushed sol, for example. In certaininstances, this is a desirable situation. For example, if the materialis particularly reactive with the sol, spraying may be the best way toavoid prolonged contact with the sol which would occur if the basematerial were soaked in, or brushed with a sol. If further materials areto be included, they can be included directly in the sol before curingcreates a gel.

The invention will be further described in the following examples, whichdo not limit the scope of the invention described in the claims.

EXAMPLES

The following examples illustrate certain embodiments of the gel-coatedmaterials of the invention, their properties, and methods of theirmanufacture.

Example 1 Preparation of a Gel-Coated Foamed Material

A gel-coated foamed silicon material was prepared. The procedurerequired handling materials that are hazardous to human health. Suitableprotective equipment was worn and appropriate precautions were taken toprevent the inhalation of any hazardous solvents, and particular carewas taken to avoid the inhalation or skin contact with nitric acid andtetraethyl orthosilicate. No open flames were allowed in the vicinityduring the procedure. The reactions were carried out in a fume hood witha filter for volatile organic compounds. The operator wore protectiveclothing, latex gloves, protective goggles and a respirator for dust andvolatile organic compounds. All transfers were one by pipette.

Ethanol (16.5 mL of 95% ethanol) and 63 mL of 98% tetraethylorthosilicate (TEOS) were added to a 150 mL polypropylene or polymethylpropylene container, and mixed well. In a separate container, 20.4 mL ofdeionized water and 1.62 g of nitric acid were mixed. The acidicsolution was added to the TEOS solution and stirred with a Teflon-coatedstirring stick for 30 minutes. The mixture was observed to become warmand then cool as the reaction was completed. This material was placed ina shallow tray and a sample of open cell silicon foam was placed in thesol. The foam was soaked in the sol long enough to fully cover allsurface, and then removed. Excess sol was removed by squeezing andwringing of the foamed material. Open cell foams may need to be squeezedwhile in the sol to ensure coverage of all exposed cell surfaces. Thefoam was left to cure overnight.

Gel-coated polyurethane was prepared similarly, and produced a somewhatmore brittle coating, although the open cell structure of the foam wasretained.

Example 2 Flammability Testing on Gel-Coated Foamed Material

Tests have been conducted on open-cell silicone foams. Foam samples werecoated with sol-gel by dipping the foam into the liquid sol, squeezingthe foam to ensure complete coverage inside the foam cells, removing thefoam from the sol, blotting off the excess sol, and setting the curedfoam aside to allow the gel coating to cure overnight. Open-celled foamstructures were found to require less curing time. It was alsodiscovered that slow curing (not accelerated by heat) resulted in lesscracking. Faster cures gave more flexible gel coatings.

Both coated and uncoated foam samples were exposed to an open flame for12 seconds. This open flame test was carried out as described in FSTM191A, which is also similar to FAR part 25, Appendix F, Part I.

Although neither silicone foam sample burned, the uncoated foam becamefriable at the area of flame contact and crumbled into sand (SiO₂) whentouched after cooling. When a single coating (approximately 1-2 microns)of sol-gel was applied and cured, there was some indication ofdiscoloration, but the foam did not become friable and remainedflexible.

Similar tests on polyurethane foams showed that an uncoated foam burnedreadily. A single gel coating also burned but at a much more controlledrate, and a double gel coating (second coating applied after curing ofthe first coating) resulted in a polyurethane foam that completelyinhibited continuous burning when the flame was removed, although thefoam did burn with the flame applied directly.

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

For example, the gel coatings described herein can also be applied tofabrics, or individual natural and man-made fibers, thereby impartingfire-, physical-, and chemical-resistance to those materials. Theapplication of the sol to fabrics or fibers would be undertakenaccording to methods which are analogous to those described for foamedpolymeric materials.

What is claimed is:
 1. A fire-resistant article of clothing comprising agel-coated material, said gel-coated material comprising: a basematerial; and at least one layer of a metal oxide- or metalalkoxide-based gel forming a network on said base material, wherein thebase material is selected from the group consisting of foamed polymericmaterial, woven fabric, nonwoven fabric, fiber, batting and matting,wherein the alkoxide can be functionalized or unfunctionalized, andwherein the gel-coated material is flame resistant.
 2. Thefire-resistant article of clothing of claim 1, wherein the article ofclothing is selected from the group consisting of a jacket, pants, vest,hat and shoes.
 3. The fire-resistant article of clothing of claim 1,further comprising encapsulated phase change material.
 4. Thefire-resistant article of clothing of claim 1, wherein the base materialis an open cell foam.
 5. The fire-resistant article of clothing of claim1, wherein the base material is a closed cell foam.
 6. Thefire-resistant article of clothing of claim 1, wherein the base materialis a hydrophilic foam.
 7. The fire-resistant article of clothing ofclaim 1, wherein the base material is a hydrophobic foam.
 8. Thefire-resistant article of clothing of claim 1, wherein the base materialis a hydrophobic foam.
 9. The fire-resistant article of clothing ofclaim 1, further comprising a phase change material.
 10. Thefire-resistant article of clothing of claim 9, wherein the phase changematerial is contained in the base material.
 11. The fire-resistantarticle of clothing of claim 9, wherein the phase change material is inencapsulated portions.
 12. A fire-resistant seat cushion comprising agel-coated material, said gel-coated material comprising: a basematerial; and at least one layer of a metal oxide- or metalalkoxide-based gel forming a network on said base material, wherein thebase material is foamed polymeric material, wherein the alkoxide can befunctionalized or unfunctionalized, and wherein the gel-coated materialis flame resistant.
 13. The fire-resistant seat cushion of claim 12,wherein the base material is an open cell foam.
 14. The fire-resistantseat cushion of claim 12, wherein the base material is a closed cellfoam.
 15. Fire-resistant insulation material comprising a gel-coatedmaterial, said gel-coated material comprising: a base material; and atleast one layer of a metal oxide- or metal alkoxide-based gel forming anetwork on said base material, wherein the base material is foamedpolymeric material, wherein the alkoxide can be functionalized orunfunctionalized, and wherein the gel-coated material is flameresistant.